New trace element deficiency diseases are investigated and new essential trace elements are being identified by means of plastic isolator systems, ultraclean environment techniques, and purified amino acid diets, in combination with sensitive methods of trace element analysis. Biological effects of tin, vanadium, fluorine, and silicon, identified as essential for growth in rats under trace element- controlled conditions, are being investigated. Organic derivatives of trace elements are being synthesized and studied for biopotency. The aim is to delineate the chemical properties of organic trace element derivatives which determine biopotency and nutritional efficacy, and to develop compounds suitable for clinical application. The metabolic pathways of trace elements are being investigated. The functions of trace elements and related dietary factors in enzyme systems and active transport are studied in order to identify their specific modes of action.